We cloned a bovine cDNA encoding the neural adhesion molecule F3 and analyzed its nucleotide sequence. The coding region consisted of 3054 bp encoding 1018 amino acid residues. The Mr calculated from the deduced amino acid sequence was 113383. Bovine F3 had 93,94 and 77% amino acid identities with the mouse, human and chicken homologs, respectively. Parts of bovine F3 protein were overporduced in Escherichia coli. The antibodies raised against the recombinant proteins in rabbits reacted specifically with F3. F3 protein was detected in cerebellum, cerebrum and spinal cord in Western blot analysis. Then we cloned a cDNA encoding rat F3 to elucidate the developmental changes of F3 in the rat brain. During postnatal development of the rat brain, cells expressing F3 mRNA appeared in the cortex, hippocampus, superior and inferior colliculi, anterior olfactory nucleus, olfactory bulb and cerebellum, whereas little was observed at postnatal day 1 (P1). Extraordinarily high expression of F3 mRNA was observed in the cerebral cortical neurons of layr 5 of at P7. The number of cells with high expression of F3 mRNA expanded to the entire region of the cerebral cortex at P14. The whole cerebrum displayd the expression at P90 in which the cortex still showed the highest expression level, although the overall signals were weak in comparison with those at P14. In the hippocampal formation, F3-expressing granule cells of the dentate gyrus were restricted to the outer aspect, then expanded to the inner aspect during development. Finally the granule cells in the entire region of the dentate gyrus transcribed F3 mRNA.We discussed the significance of the expression pattern of F3 mRNA during development.